RFR: 8350605: assert(!heap->is_uncommit_in_progress()) failed: Cannot uncommit bitmaps while resetting them

[William Kemper]

The protocol which is meant to prevent regions from being uncommitted while their bitmaps are being reset may fail. This happens when the control thread attempts to wait for the uncommit thread to finish, but the uncommit thread has not yet indicated that it has started.

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Commit messages:
 - Use lock to protect in progress flag, remove unnecessary stop lock and flag

Changes: https://git.openjdk.org/jdk/pull/23760/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23760&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8350605
  Stats: 74 lines in 2 files changed: 36 ins; 24 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/23760.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23760/head:pull/23760

PR: https://git.openjdk.org/jdk/pull/23760